Joint Research Project with Japan on the Catchment Analysis Lead organization: Acid Deposition and Oxidant Research Center Organizations in the participating countries: Niigata University, Japan Niigata Prefectural Institute of Public Health and Environmental Sciences, Japan 1. Introduction The data of the catchment-scale analysis has not been enough accumulated even in Japan, especially in the area along the Sea of Japan, which receives a high level of atmospheric deposition and shows its clear seasonality. A project was started in 2002 to accumulate experience and knowledge on the catchment-scale analysis in this area. Moreover, the experience may be informative for implementation of similar projects in Thailand and Malaysia and for the future catchment-scale monitoring in EANET. This report was prepared based on two scientific papers published in international journals. 2. Objectives The project was carried out with the following final objectives: To estimate effects of acidic deposition on the forested catchment in the area along the Sea of Japan To develop a monitoring guideline for the catchment analysis for future EANET monitoring 3. Methods The study site was established in 2002 in a small forested catchment (approximately 3.84 ha) near the Sea of Japan in the northern part of Shibata City (the former Kajikawa Village), Niigata Prefecture, Japan (Fig. 1). Rainfall (RF), throughfall (TF) and stemflow (SF) collectors were installed in the study site as shown in Fig. 1. Rainwater samples were collected at intervals of about 4 weeks until 2007 and then ever 2 weeks thereafter. A weir was installed at the Figure 1 Study site and layout of the collectors. bottom of the catchment, where the stream water (SW) was collected at intervals of roughly 2 weeks. 119
Inorganic constituents in the water samples were determined by ion chromatography. Intensive sampling of soil, Japanese cedar leaves, and SW was carried out occasionally. 4. Outcomes of the project The study catchment exhibited distinct seasonality in atmospheric deposition (Fig. 2). The fluxes for Na + and Cl from RF increased from late autumn to midwinter, and then decreased in the spring. Seasonal trends were observed for the fluxes of SO 2 4, Ca 2+, and Mg 2+, which were comparable to those of Na + and Cl (Sase et al., 2008; Kamisako et al., in press). Fluxes of NO - 3, NH + 4, and K + did not show clear seasonal trends, especially for TF and SF, suggesting canopy interactions, while those of NO - 3 and K + showed weak trends (Sase et al., 2008). Figure 2 Seasonal changes of atmospheric depositions from rainfall outside the canopy (a) and from throughfall and stemflow (b) (Kamisako et al. in press). Leaf surface properties deteriorated gradually with leaf aging. The amount of epicuticular wax increased during the development of the leaves, and then decreased gradually with leaf age. The contact angle (CA) of water droplets on the leaf surface decreased gradually after leaf expansion/growth in both 0-y and 1-y leaves, as shown in Fig.3, but the decrease in CA for 0-y leaves was greater. The CA of 0-y leaves was higher than the 1-y leaves (p < 0.001). The leaching rate of K + by the exposure test to artificial fog water was significantly higher in 1-y leaves than in 0-y leaves (p < 0.001). Changes of leaf surface properties may affect canopy interactions (Sase et al., 2008). 120
Figure 3 A sample measurement of the contact angles (CAs) of a water droplet on the surface of a 0-y leaf in June (a) and a 1-y leaf in November (b). CA was calculated based on the height (H) and basal diameter (BD) of the droplet according to the following equation. CA = 2tan 1 [H/(BD/2)]*(180/π). (Sase et al., 2008). The concentrations and fluxes of ions from TF in the snow-free seasons were compared with CA to elucidate the effects of leaf wettability on ion transport between droplets of rainwater and the surface of the leaf. The concentration of K + increased with increase of wettability, + while the concentration of NH 4 decreased (Fig. 4a). The net fluxes of NO 3 and NH + 4 from TF decreased with increase of wettability (Fig. 4b), but the correlation coefficient was larger for NH + 4 than for NO 3. Similar correlations were also observed with the CA of 0-y leaves, showing slightly weaker correlations for NO 3 (r = 0.582, p = + 0.011) and NH 4 (r = 0.702, p = 0.001). Leaf surface properties, leaf wettability in particular, may be one of regulatory factors for the leaching of K + and uptake and/or consumption of nitrogen compounds on the forest canopy, which Figure 4 The relationship between contact angle and concentrations of K + and NH + 4 in throughfall (a) and net flux of nitrogen compounds by throughfall (b) (Sase et al., 2008). 121
accelerates ion exchange on the surface (Sase et al., 2008). Annual dissolved inorganic nitrogen inputs in RF and in TF + SF were 17.7 and 17.9 kg N ha -1 y -1, respectively, which exceeded previously published thresholds in Europe and the U.S. (i.e., the values at which these inputs increased NO - 3 levels in SW) and equaled the highest level of nitrogen deposition previously reported in Japan. The NO - 3 concentration in SW decreased slightly in summer, indicating biological uptake of N during the growing season. However, the lowest NO - 3 concentrations observed in the summer were still relatively high, equaling approximately 30 µeq L -1. Moreover, temporary acidification of SW was observed with - high NO 3 concentrations during heavy rain events (Fig. 5). Figure 5 Changes in the stream water properties during a heavy rainfall event in June 2005 (Kamisako et al., in press). Table 1 Annual fluxes of inorganic constituents in the study site (Kamisako et al. in press) The H + inputs were well neutralized in the soil, whereas significant quantities of base cations, such as Ca 2+ and Mg 2+, were leached into SW (Table 1), suggesting that the acid neutralizing capacity of the soil has gradually decreased as a result of H + consumption in the soil. 5. Conclusion The study area may experience a relatively direct effect of seasonal winds from the Sea of Japan. 122
However, seasonal changes in the flux and net flux of TF+SF suggest that the leaching of K + and uptake and/or consumption of nitrogen compounds, especially NH + 4, is occurring on the forest canopy. Estimation of dry deposition fluxes is necessary for precise discussion of total deposition in the forest area, taking the canopy interactions into account. Moreover, N deposition in the study site equaled the highest level observed in Japan, which would cause unused N to leach into SW even during the growing season. The magnitude of the N deposition would certainly contribute to the high NO - 3 concentrations observed in SW and the temporary acidification that was observed during intense rainfall events. References Kamisako, M., Sase, H., Matsui, T., Suzuki, H., Takahashi, A., Oida, T., Nakata, M., Totsuka, T. & Ueda, H. 2008. Seasonal and annual fluxes of inorganic constituents in a small catchment of a Japanese cedar forest near the Sea of Japan. Water, Air, & Soil Pollution, doi: 10.1007/s11270-008-9726-8. Sase, H., Takahashi, A., Sato, M., Kobayashi, H., Nakata, M. & Totsuka, T. 2008. Seasonal variation in the atmospheric deposition of inorganic constituents and canopy interactions in a Japanese cedar forest. Environmental Pollution 152: 1-10. 123